Human Anatomy - H. I. Koliadenko 2009

The Doctrine of Viscera (Splanchnology)
Respiratory System (Respiratory Organs)
Development of Respiratory Organs

Phylogeny of the respiratory Organs. In the fourth week of embryonic development, a groove forms in the cervical region of the primitive gut, which transforms into a tubular outgrowth lying parallel to the digestive tract. At the upper end of this outgrowth, the laryngeal cartilages are laid down, below which the rudiments of the tracheal rings begin to form. In a six-week-old embryo, the lower end of the tube bifurcates. A bulbous expansion develops at each end of the tube, representing the primordium of the Bronchi and Lungs. By the sixth month, The formation of all respiratory passages is complete. The epithelial tubes branch out to form the bronchial epithelium, while the surrounding mesenchyme gives rise to the bronchial walls, Connective Tissue, Cartilage, and smooth Muscle. The lungs themselves are formed by the sixth month. The terminal dilations develop into alveolar ducts, within the walls of which secondary sacs—alveoli—appear, where gas exchange takes place after birth.

The primary respiratory tube is covered by mesoderm, from which two pleural membranes—the visceral and parietal Pleura—are formed.

Ontogeny of the respiratory organs. In children, the nasal passages are significantly narrower than in adults, and they reach their final development by the age of 14–15. As a result, infections can invade the body through children's nasal passages much more easily than in adults. Children tend to breathe through their mouths more often than adults (especially at low temperatures), which leads to chilling of the respiratory tract and the penetration of microorganisms and dust particles into the lungs, thereby causing respiratory inflammation.

During ontogeny, structural changes also occur in the Larynx. In newborns, it is short and wide, and its upper boundary is located three vertebrae higher than in an adult. The glottis in children is narrower than in adults, and the vocal cords grow intensively During the first year of life. Sexual Dimorphism in voice characteristics becomes established around the age of 12. At this stage, girls have shorter vocal cords than boys, which results in a higher voice pitch. In 12–13-year-old boys, the length of the vocal cords is 13–14 mm, whereas in girls it is 9–10 mm; in adult men, it reaches 22–25 mm, and in women, 18–20 mm.

The Muscles of the larynx develop intensively between the ages of 7 and 12, a process that concludes by age 20. The mucous membrane of the larynx in children is more sensitive to irritants (microorganisms, toxins) than in adults, which makes inflammation more frequent in childhood. During this period, the vocal cords should be protected from excessive strain, shouting, and loud singing, as this can negatively affect the strength and timbre of the voice in adulthood. With age, the COMPOSITION OF THE laryngeal cartilage changes, and ossified areas appear. In elderly individuals, all cartilages except the epiglottis become ossified.

In children, the Trachea and Bronchi develop gradually, growing in parallel with the trunk. The lumen of these organs is narrower in children than in adults, and the cartilages are not yet fully ossified. The muscular and elastic fibers are insufficiently developed, and the mucous membrane of the trachea and bronchi is very delicate and richly supplied with Blood Vessels. In a newborn, the trachea is cone-shaped and wider toward the larynx, and its membranous wall is broad.

The lungs develop from the first years of a child's life, and by the age of 18, their mass increases nearly 8-fold. Growth is particularly intense during the first year of life, when lung mass increases 4-fold compared to that of newborns. Starting from age 7, the alveoli grow rapidly, doubling in size by age 14 compared to newborn alveoli. An adult human lung contains about 700 million alveoli, ensuring rapid gas exchange. The total alveolar surface area in adults is 100–120 m².

The lungs of a newborn are pink in color. With age, they acquire a grayish-pink hue due to the incomplete clearance of dust particles from the lung tissue. In smokers, the function of the respiratory apparatus is drastically impaired.

The mass of a newborn's lungs is 50 g, at 1 year it is 150 g, at 12 years 500 g, and in an adult it is approximately 1 kg.

Lung tissue is more elastic in children.

The tidal volume in a newborn is 20 cm³, at 1 year 70 cm³, at 5 years 150 cm³, at 12 years 260 cm³, and in adults it reaches 500–600 cm³.

Vital capacity in 7-year-old children is 1400 ml, at 9 years 1700 ml, at 14 years 2700 ml, and at 16 years and in adulthood it ranges from 3000 to 4000 ml.

The respiratory rate in newborns is 40–60 breaths per minute, at 7–9 years 20–22 breaths, and at 15–16 years, as in adults, 16–18 breaths.

The Respiratory Muscles in children are smaller, and the dome of the Diaphragm is higher than in adults, which places a heavier workload on the lungs and Heart. In 8-year-old children, the work of the respiratory muscles is 2.5 times less efficient than in adults. The endurance and functional capacity of the respiratory muscles grow intensively up to 13–14 years of age in girls and up to 17 years in boys. Consequently, adolescence is the most promising period for The Development of the respiratory organs. Therefore, physical exercises should be widely encouraged for children of this age. Under METABOLISM/18.html">The Influence of regular physical training and sports, all Organs of the Respiratory system develop effectively, achieving physiological maturity sooner, while involutional processes in old age are delayed.

In well-trained individuals, vital capacity increases dramatically (up to 6000–8000 cm³) due to an expansion of the total alveolar surface area, with the lung surface area reaching 200–220 m². The respiratory rate in trained individuals decreases and can drop to 10–12 breaths per minute. Consequently, at rest, the respiratory apparatus of a trained person operates much more efficiently than that of an untrained person, and performs with greater productivity during intense physical exertion.

Newborns exhibit an abdominal type of breathing. By the age of 7, the thoracic type of breathing is clearly defined. Starting around age 10, sex-related breathing differences begin to emerge: girls retain the thoracic type of breathing, whereas boys develop the abdominal type.